A conveyor-belt roller assembly is a roller like device, which fits inside either end of a cylindrical roller tube of a conveyor-belt, and carries the cylindrical roller tube while being mounting on and rotating around an inner shaft, thus allowing rotation of the cylindrical roller tube. It is well known that conveyor-belt roller assemblies must withstand incredible pressure from the great loads that they carry. Other characteristics of the roller assemblies are that they must withstand severe bombardment from the elements, function within a potentially hazardous environment and remain as reliable and maintenance free as possible so as to be safe when used and to be financially beneficial. Although the requirements for a conveyor-belt roller assembly are known, producing an assembly that complies with all of the above parameters has yet to be accomplished.
One such attempt is U.S. Pat. No. 5,261,528 which discloses a conveyor-belt roller assembly that is enclosed with a ring assembly. The cylinder operates on ball bearings and uses a straight labyrinth seal in conjunction with a felt insert sealing the bearings from the atmosphere while providing a lubricating environment for the components sealed within the roller. The entire assembly, like most, is press fit into a cylindrical shell of the roller. However, the load-bearing component of the assembly comprises very few strengthening characteristics and is too easily broken under heavy load. The outermost surface of the assembly exposed to the elements rotates with the head and no protection barrier is provided to prevent the outside environment from coming into contact with the rotating part and potentially stopping or interfering with the assembly's rotation. The stoppage of rotation is extremely costly in that there is potential for damage to be caused to the cylindrical roller and roller assembly as well as to the belt itself. Shutting down the conveyor-belt to replace broken roller assemblies can result in a huge financial penalty, therefore protection of the roller assembly and the rotating parts is extremely important.
Another attempt is U.S. Pat. No. 5,383,549 which discloses a conveyor-belt cylinder assembly that is sealed with a straight labyrinth seal. As in standard construction of a roller assembly, ball bearings are once again used as a low friction way of rotating the assembly around a fixed inner shaft. A small dust cap is fitted over the end of the straight labyrinth seal to help prevent dust and dirt buildup. However, the base of the assembly, which in this particular instance represents the load-bearing portion of the assembly, has little or no strengthening characteristics and can support only a limited load. In addition, the exterior rotating end of the assembly is open to the outside environment, and nothing prevents the external environment from coming into contact with and disrupting or stopping the rotation of the roller assembly.
Up until now, the standard material used in the construction of conveyor-belt roller assemblies was a variety of high-strength, fire resistant plastic materials such as ABS.TM., sometimes in conjunction with metal and urethane components. Although the older materials functioned in a capacity, the capacity was limited. An improved material is used in the conveyor-belt roller assembly of the present invention. More specifically, for example, the inner labyrinth seal and the polycap are preferably made of a composition consisting of 30% glass filled polypropylene. The 30% glass filled polypropylene increases strength and is far more heat resistant as, for example, the following figures indicate:
30% Glass Filled Property Data Unit Polypropylene Tensile Strength psi 12,000 Elongation % 3.5 Tensile Modulus psi .times. 10.sup.6 8.5 Flexural Strength psi 16,000 Flexural Modulus psi .times. 10.sup.6 8.0 Izod Impact (1/4") ft-lb/in 1.7 Rockwell Hardness -- R105-115 Specific Gravity -- 1.13 Water absorption, 24 hrs % 0.03 Linear Mold Shrinkage 1/8" Average Section in/in 0.003 1/4" Average Section in/in 0.004 Deflection Temp. Under Load @ 264 psi .degree. C. 152 @ 66 psi .degree. C. 159
Furthermore, in prior art assemblies, for example the assembly shown in U.S. Pat. No. 5,383,549, the labyrinth seal is a straight shaped seal and requires multiple assembly steps. The present invention has overcome this need for multiple steps in the assembly by tapering the inner labyrinth seal, thereby making it possible for the labyrinth seal to be press locked into position.
An additional problem of earlier models is that the exterior surface of the conveyor-belt roller assembly rotated and was exposed to the outside environment. This is dangerous in that outside elements can come into contact with the roller assembly and interfere with its rotation, possibly even stopping the rotation. The assembly was also unprotected from the elements and damage other than rotational damage could occur such that, for example, a seal could be broken or the outer and inner working components could be bent or damaged. The present invention overcomes this by the addition of an anti-lock shield used in conjunction with a rubber dust shield. The anti-lock shield is positioned outside of the roller assembly and fixed directly to the inner shaft, thereby preventing the anti-lock shield from rotating in conjunction with the roller assembly and roller. The outside leading edge of the anti-lock shield is substantially flush with the cylindrical roller making it nearly impossible for the roller assembly to come into contact with outside elements. For even more preventative measures, a rubber dust shield fits on the inside of the anti-lock shield in between the anti-lock shield and the inner workings of the roller assembly, specifically the polycap, making it even more unlikely for any outside dust or debris to penetrate the assembly. This causes an increase in the reliability of the roller assembly and decreases maintenance costs and downtime of the conveyor-belt apparatus.
Although the present invention improves in many areas, the most significant improvement comes in the polycap component, which is the main load-bearing component of the roller assembly. In the past, roller assemblies would break and crack under increased load. The current invention has overcome this by creating an all new polycap which comprises the main element of the roller assembly. The roller assembly is fitted into a cylindrical roller which guides a conveyor-belt and rotates to allow movement of the conveyor-belt. The roller assembly is fitted onto a stationary inner shaft and held in place by the polycap. Force of a load is input from the conveyor-belt through the roller and into the roller assembly where the polycap takes the force of the load. The polycap is designed, preferably out of 30% glass filled polypropylene, with two deep annular rings positioned on its posterior side toward the outer edge. Each annular ring is bridged by, preferably, sixteen strengthening ribs. The ribs are offset so that no two ribs are inline. This greatly increases the strength of the roller assembly and allows for increased load on the roller and therefore the conveyor-belt.